Various drying techniques are known in the art. Example techniques include exhaust pipe techniques, condenser-based techniques, heat-exchanger-based techniques and techniques based on heat pumps. Such techniques are implemented, for example, in laundry dryers. The various drying techniques differ from one another in parameters such as cost and energy efficiency.
For example, U.S. Pat. No. 8,438,751, whose disclosure is incorporated herein by reference, describes a dryer having a drying chamber for items to be dried and a process air duct in which are located a heater for heating the process air, a blower for driving the process air from the heater through the drying chamber, and a heat exchanger arrangement. Via the heat exchanger arrangement, heat can be withdrawn from the process air flowing away from the drying chamber, and the process air flowing toward the heater can be fed to the heat exchanger.
U.S. Pat. No. 8,240,064, whose disclosure is incorporated herein by reference, describes a dryer that includes a drying chamber for articles to be dried, a supply air duct, a process air duct, a heater in the process air duct for heating process air, a blower that guides the heated process air over the articles to be dried, an exhaust air duct that directs exhaust air to an exhaust air outlet, and an internally and/or externally cleanable lint filter in a recirculated air duct that splits at a branching-off point from the process air duct to the heater and the exhaust air duct which leads to the exhaust air outlet. The recirculated air duct joins the supply air duct upstream of the heater.
U.S. Pat. No. 8,353,115, whose disclosure is incorporated herein by reference, describes an exhaust air dryer that includes a process airflow entering from outside as supply air, which removes moisture from laundry introduced in a treatment compartment and which emerges to the outside as exhaust air through an air outlet, a heat exchanger between the treatment compartment and the air outlet, and an active heat pump seen in the airflow direction, which removes heat from the process airflow, while forming condensate, and at the same time heats the incoming air.
U.S. Patent Application Publication 2012/0030959, whose disclosure is incorporated herein by reference, describes a rotary drum dryer with heat recycling and water collecting function. The dryer dries rolling clothes by electric heating thermal energy. A heat exchanging unit with heat recycling function is further installed between the room temperature air flow and the discharged hot air, for preheating the intake air flow by the thermal energy of the discharged hot air through the heat exchanging unit. Moisture is converted into a liquid state via a cooling effect generated through heat exchanging between water-contained hot air and colder air and is collected.
U.S. Pat. No. 8,572,862, whose disclosure is incorporated herein by reference, describes a drying apparatus that includes a drum and an open-loop airflow pathway originating at an ambient air inlet, passing through the drum, and terminating at an exhaust outlet. A passive heat exchanger is included for passively transferring heat from air flowing from the drum toward the exhaust outlet to air flowing from the ambient air inlet toward the drum. A heat pump is also included for actively transferring heat from air flowing from the passive heat exchanger toward the exhaust outlet to air flowing from the passive heat exchanger toward the drum. A heating element is also included for further heating air flowing from the heat pump toward the drum.
U.S. Patent Application Publication 2012/0233876, whose disclosure is incorporated herein by reference, describes a home laundry dryer in which both the fresh air entering a laundry drum and the air exhausted from the drum pass through thermal recovery ducting. The dryer heat recovery system has concentric ducting including a high temperature passage through which the exhaust air flows and a separate low temperature passage through which the entering air flows. Heat from the exhausted air is transferred from the high temperature passage to the entering air in the low temperature passage. This heat transfer lowers the energy required to raise the entering air to a desired drying temperature. The dryer ducting is designed to have an outer diameter equivalent to standard size ducting on home dryers.
European Patents EP 2576889 and EP 2576888, whose disclosures are incorporated herein by reference, describe thermoelectric heat pump laundry dryers. U.S. Pat. No. 7,526,879, whose disclosure is incorporated herein by reference, describes a drum washing machine and a clothes dryer equipped with a thermoelectric module. The thermoelectric module includes a heat absorption side and a heat dissipation side. The heat absorption side is disposed at a hot air flowing passage.
U.S. Pat. No. 4,154,003, whose disclosure is incorporated herein by reference, describes a combination washer-dryer comprised of an inner and outer container that are spaced apart so as to form a condensation chamber therebetween. A cooling medium and moist air withdrawn from the inner drying container are simultaneously forced through that chamber which cools the air and causes moisture contained therein to be condensed and thus separatable from the air. Additional condensation and water separators can be employed to further treat the circulating air prior to that air being reheated and returned to the inner drying container.